1. Field of the Invention
The present invention relates to a system and method for providing pressurized oil during non-feathered in-flight shutdown conditions in a variable-pitch aircraft propeller engine.
2. Description of the Prior Art
Propeller control systems for turboprop engines normally employ pressurized oil as a means of system actuation. The source of this pressurized oil is usually from a positive displacement or other pump which is driven from the propeller reduction gearbox (RGB) of the engine. The oil supply for this pump is typically provided by the RGB lubrication system, which is sized to ensure that the oil supply requirements of the propeller pump are satisfied during normal engine operating conditions.
During in-flight engine shutdown conditions, it may be required to operate the propeller in a non-feathered or rotating condition and under these conditions it is desirable to have a functioning propeller control system.
During non-feathered operation, it may not be possible for the RGB lubrication system to maintain an adequate oil supply to the propeller pump, because during engine shutdown conditions, the engine spool driving the propeller pump is either stationary or rotating at very low speeds and, hence, unlikely to provide the required pressurized oil flow required at the propeller pump inlet. A low oil supply obviously prejudices operation of the propeller system during in-flight shutdown, non-feathered conditions, and accordingly there is a need to provide an improved manner of supply oil to the propeller system.